This invention relates generally to bottom hole assemblies for drilling wellbores and more particularly to the use of magnetometers and other sensors to determine wellbore direction during the drilling of the wellbores.
To obtain hydrocarbons such as oil and gas, wellbores (also referred to as boreholes) are drilled by rotating a drill bit attached at the end of a drilling assembly generally referred to as the “bottom hole assembly” (BHA) or the “drilling assembly.” A large portion of the current drilling activity involves drilling highly deviated and substantially horizontal wellbores to increase production (e.g., hydrocarbon production) and/or to withdraw additional fluids from the earth's formations. In the case of hydrocarbon wells, the wellbore path of such wells is carefully planned prior to drilling such wellbores utilizing seismic maps of the earth's subsurface and well data from previously drilled wellbores in the associated oil fields. Due to the very high cost of drilling such wellbores and the need to precisely place such wellbores in the reservoirs, it is desirable to frequently determine the position and direction of the drilling assembly and thus the drill bit during drilling of the wellbores. Such information is utilized, among other things, to monitor and adjust the drilling direction of the wellbores. It should be noted that the terms “wellbore” and “borehole” are used interchangeably in the present document.